The present invention pertains to a coated cemented carbide insert for machining of steels or stainless steel when a high wear resistance combined with a high edge toughness are required.
In typical milling operations, the thermal load on the insert will vary over time, something that often induces thermal tension and subsequently may generate thermally induced cracks in the coatings. This is especially a concern with cooled/wet operations where the thermal variations are more pronounced than in dry operations.
A common wear mechanism in milling is cracking, followed by chipping or small fragments of the cutting edge loosening from the rest of the substrate. Increasing the edge toughness is thus of great importance to increase tool lifetime. One possible solution to decrease the risk of thermal cracking—as well as cracking for various other reasons—is to use a multilayered coating. The multilayered coating is expected to act as a crack inhibitor as an initial crack going down the coating may be redirected at any sublayer interface. Another benefit of multilayer coatings is expected to show up when hard, wear resistant layers are interlaid with a softer sublayer. The softer layer may be able to absorb shocks and thus inhibit cracks from penetrating the whole coating.
WO 98/48072 relates to a cutting tool comprising a body of sintered cemented carbide, ceramic or high speed steel on which at least on the functional parts of the surface of the body, a thin, adherent, hard and wear resistant coating is applied. The coating comprises a laminar, multilayered structure of refractory compounds in polycrystalline, non-repetitive form MX+NX+MX+NX . . . where the alternating layers MX and NX are composed of metal nitrides or metal carbides. The sequence of individual layer thicknesses is essentially aperiodic throughout the entire multilayered structure.